Data Transmission

Figure 10: Telegram Format Fields in KNX/EIB

As soon as an event occurs, it is detected by a sensor, which in response sends a telegram. This event can be random, e.g detection of presence, or it can be cyclic, turning the lights every day at a given hour. The telegram is sent following the CSMA/CA protocol. If the receiver gets the information and is correct, it responds with an acknowledgment, ACK, otherwise there is no response at all. When there is no response, retransmission takes place automatically for a given number of iteration.

The telegram is formed by seven fields, six for control requirements and one for the data, as shown in figure 10. At 9600bps, the transmission of a byte needs 1d.35ms, and the transmission of a complete telegram needs between 20 and 40ms.

Once the installation is finished and the conventional communication takes place, the group address will be included within the destination field, which allows sending control orders to sensors and actuators. These orders are included in the data field and are defined by the EIB Interworking Standard EIS depending on their size and function.

The EIS contains the data for each function that has been assigned to the communication objects. According to the standard, there are seven different communication objects, each one assigned to a type of control action (communication, light regulation, sending an absolute value, floating point values, etc.). In this way it is possible to guarantee compatibility among devices from different manufactures.

Programming the physical address to the device according to the topology that has been used.

- Load the libraries, data bases, plugins and utilities created by the manufactures for the specific devices into the ETS.

- Configure the application, based on the parameters that each component will need.

- Assign group addressing between devices to unify sensors, actuators, controllers and communication objects.

- Load the programmed application of ETS into the installation.